HI 🙌 David,
All IBAN numbers are composed by Letters and Numbers.
Take a look at this web service:
If you looking for your bank account number (which is not the full IBAN), always from the above web service, once you pick the IBAN of your country, it describes how to derive your bank account number.
Example for The Netherlands:
Standard IBAN Format in Netherlands
Below is the typical IBAN for Netherlands. It contains 18 characters. Below you will find a detailed breakdown of the IBAN structure in Netherlands.
2 letters ISO country code
2 digits IBAN check digits
4 characters SWIFT/BIC code
10 digits account number
NL 91 ABNA 0417164300
0417164300 is the bank account.
I hope this answers your question 🙏
Have a great day 🌈